<?php
/**
 * Class used internally by Diff to actually compute the diffs.  This class
 * uses the xdiff PECL package (http://pecl.php.net/package/xdiff) to compute
 * the differences between the two input arrays.
 *
 * @author  Jon Parise <jon@horde.org>
 * @package Text_Diff
 *
 * @access private
 */
class Text_Diff_Engine_xdiff {

		function diff($from_lines, $to_lines)
		{
				array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
				array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

				/* Convert the two input arrays into strings for xdiff processing. */
				$from_string = implode("\n", $from_lines);
				$to_string = implode("\n", $to_lines);

				/* Diff the two strings and convert the result to an array. */
				$diff = xdiff_string_diff($from_string, $to_string, count($to_lines));
				$diff = explode("\n", $diff);

				/* Walk through the diff one line at a time.  We build the $edits
 				* array of diff operations by reading the first character of the
 				* xdiff output (which is in the "unified diff" format).
 				*
 				* Note that we don't have enough information to detect "changed"
 				* lines using this approach, so we can't add Text_Diff_Op_changed
 				* instances to the $edits array.  The result is still perfectly
 				* valid, albeit a little less descriptive and efficient. */
				$edits = array();
				foreach ($diff as $line) {
						switch ($line[0]) {
						case ' ':
								$edits[] = &new Text_Diff_Op_copy(array(substr($line, 1)));
								break;

						case '+':
								$edits[] = &new Text_Diff_Op_add(array(substr($line, 1)));
								break;

						case '-':
								$edits[] = &new Text_Diff_Op_delete(array(substr($line, 1)));
								break;
						}
				}

				return $edits;
		}

}
